When a known asteroid passed within 28,000 kilometers of Earth on February 15, astronomers hoped it would serve as a wake-up call about the danger of meteorite impacts. As it turned out, astronomers got more than they had bargained for. On that same day, a 19-meter-wide space rock plowed through the atmosphere and exploded over southwestern Russia near Chelyabinsk, shattering windows and causing more than 1,600 injuries. The largest recorded meteor since 1908 spurred scientists and governme...